Any steam sterilization process used to sterilize medical and hospital equipment cannot be effective unless the steam sterilant has been in contact with all surfaces of the materials being sterilized for the proper combination of time, temperature, and steam quality. In steam sterilizers, such as pre-vacuum steam sterilizers and gravity displacement steam sterilizers, the process of sterilization is conducted in three main phases. In the first phase, air is removed, including air trapped within any porous materials being processed. The second phase is a sterilizing stage, in which the load is subjected to steam under pressure for a recognized, predetermined combination of time and temperature to effect sterilization. The third phase is a drying phase in which condensation formed during the first two phases is removed by evacuating the chamber.
Air removal from the sterilization chamber may be achieved in a number of ways. For example, in a gravity displacement steam sterilizer, the principle of gravity displacement is utilized, in which steam entering at the top gradually displaces the air through a valve in the base of the chamber. Alternatively, in a pre-vacuum steam sterilizer, air is removed forcibly by deep evacuation of the chamber or by a combination of evacuation and steam injection at either subatmospheric and/or superatmospheric pressures.
Any air that is not removed from the sterilizer during the air removal phase of the cycle or which leaks into the sterilizer during a subatmospheric pressure stage due to faulty gaskets, valves or seals may form air pockets within any porous materials present. These air pockets will create a barrier to steam penetration, thereby preventing adequate sterilizing conditions being achieved for all surfaces of the materials being sterilized during the sterilizing phase. This is particularly true when porous materials such as hospital linens or fabrics are being sterilized since the air pockets prohibit the steam from reaching the interior layers of such materials. Other particularly problematic objects to be sterilized are medical devices having elongated and/or long hollow spaces, e.g. tubing, catheters, syringe needles, which are not easily penetrated by the steam. As a result, proper sterilization may not occur. Therefore, there is a need for a device and a method for determining the efficacy of sterilization cycles in sterilizers which operate by detecting whether there has been sufficient sterilant penetration.